Electromagnetic radiation detectors conventionally consist of a circuit for detecting said waves to be detected, and are therefore sensitive to the corresponding wavelength range, converting an electromagnetic signal to an electrical signal in a manner known per se. This detection circuit is associated with an electronic read circuit, intended to convert the electrical signals issuing from the detection circuit to make them suitable for undergoing a subsequent processing, particularly after amplification.
Also in a manner known per se, the mechanical and electrical connection between the detection circuit and the read circuit takes place by the technology called hybridization by bumps or microbumps, also referred to as “Flip Chip”. These bumps or microbumps are made from indium, or even from tin/lead alloy.
The detection circuit conventionally comprises a material that is transparent to or a poor absorber of the radiation to be detected, and consists for example of CdTe, CdZnTe, or even germanium, on which a thin absorbent layer of HgCdTe constituting the actual detection circuit is deposited by epitaxy (in liquid phase, vapor phase, or by molecular jet).
The read circuit is usually made from silicon.
These various technologies are fully controlled today.
However, the developments observed in the field of detection, and more particularly in the space field, require the use of very large focal planes, typically larger than 100 millimeters. Concerning the actual detection element, this demands the use of several elementary detection modules joined to one another or placed in a staggered arrangement. In fact, such detection systems have a number of requirements associated in particular with the focusing, the reconstitution of a very large detection array . . . , which accordingly impose limitations on the relative positioning of the various elementary modules, on the one hand in the two dimensions of the plane in which they are inscribed (sides X, Y), and on the other, on the dispersion along side Z, that is in the direction perpendicular to the plane of the various diodes constituting the focal plane.
Among these technical solutions proposed so far, the earliest proposed the mechanical attachment of the various elementary modules constituting the focal plane by screwing or clamping to the interconnection array or substrate. FIG. 1 shows an illustration of this technology. Numeral 1 indicates the interconnection substrate and numeral 2 the various elementary modules mounted in a staggered arrangement, which constitute the detection array.
Each of these modules 2 comprises a read circuit 3, and in the example described two detection circuits 4, 5 correspond to two different wavelength ranges. Each of these modules 2 is bonded to a transfer pad 6, typically made from molybdenum, since the screwing or clamping 7 cannot be carried out directly on the read circuit.
Also proposed (see FIG. 2) was a mechanical maintenance of the various elementary modules by bonding. According to this technology, each of the elementary modules 2 is positioned on the interconnection array or substrate 1, and is maintained in position by polymerization of a bed of adhesive deposited between the read circuit 3 and said interconnection substrate.
Also proposed (see FIG. 3), was a mode for attaching the elementary modules 2 to the interconnection substrate 1 by hybridization, that also uses the “Flip chip” technology.
In this case, the position maintenance can be reinforced by curing of an adhesive that can be caused to migrate between the read circuit 3 and the interconnection circuit 1 (underfilling)—this can only constitute an optional reinforcement of the position maintenance.
Regardless of the technology employed, a difficulty arises when it is observed that one or more of the detectors no longer supply the required performance, particularly due to an accidental degradation, or even when a change in performance of one or more elementary modules is observed between the sorting phase of said modules and the test phase after final mounting on the interconnection substrate.
In fact, the replacement of such a defective elementary module must not affect the adjacent modules. Moreover, the installation of a new module must meet the requisite electro-optical specifications.
Finally, the geometric specifications must be preserved after the replacement of such an elementary module, in particular for the final focal plane, the X, Y and Z positioning of the photosites.
No method is available today for replacing a defective elementary module in this way. It is the object of the present invention to propose such a method.